Nica et al. Chemistry Central Journal 2012, 6:55 http://journal.chemistrycentral.com/content/6/1/55 RESEARCH ARTICLE Open Access Bioaccumulative and conchological assessment of heavy metal transfer in a soil-plant-snail food chain Dragos V Nica1, Marian Bura1, Iosif Gergen2, Monica Harmanescu3 and Despina-Maria Bordean2* Abstract Background: Copper (Cu), zinc (Zn), cadmium (Cd), and lead (Pb) can pose serious threats to environmental health because they tend to bioaccumulate in terrestrial ecosystems. We investigated under field conditions the transfer of these heavy metals in a soil-plant-snail food chain in Banat area, Romania. The main goal of this paper was to assess the Roman snail (Helix pomatia) usefulness in environmental monitoring as bioindicator of heavy metal accumulation. Eight sampling sites, selected by different history of heavy metal (HM) exposure, were chosen to be sampled for soil, nettle leaves, and newly matured snails. This study also aimed to identify the putative effects of HM accumulation in the environment on phenotypic variability in selected shell features, which included shell height (SH), relative shell height (RSH), and whorl number (WN). Results: Significantly higher amounts of HMs were accumulated in snail hepatopancreas and not in foot. Cu, Zn, and Cd have biomagnified in the snail body, particularly in the hepatopancreas. In contrast, Pb decreased when going up into the food chain. Zn, Cd, and Pb correlated highly with each other at all levels of the investigated food chain. Zn and Pb exhibited an effective soil–plant transfer, whereas in the snail body only foot Cu concentration was correlated with that in soil. There were significant differences among sampling sites for WN, SH, and RSH when compared with reference snails. WN was strongly correlated with Cd and Pb concentrations in nettle leaves but not with Cu and Zn. SH was independent of HM concentrations in soil, snail hepatopancreas, and foot. However, SH correlated negatively with nettle leaves concentrations for each HM except Cu. In contrast, RSH correlated significantly only with Pb concentration in hepatopancreas. Conclusions: The snail hepatopancreas accumulates high amounts of HMs, and therefore, this organ can function as a reliable biomarker for tracking HM bioavailability in soil. Long-term exposure to HMs via contaminated food might influence the variability of shell traits in snail populations. Therefore, our results highlight the Roman snail (Helix pomatia) potential to be used in environmental monitoring studies as bioindicator of HM pollution. Keywords: Helix pomatia, Bioindicator, Environmental monitoring, Heavy metal accumulation, Food chain, Risk assessment Background monitoring relies on specific analytical techniques (e.g., The growing awareness and concerns about the impact titrimetric methods, atomic spectroscopy, mass spec- of global pollution on human lives and health have tri- trometry, chromatography) to measure the precise level ggered scientists interest to characterize and monitor of specific pollutants in natural environments, but it the quality of the biota. Environmental monitoring is cannot account for the cumulative impact of complex defined as “a time series of measurements of physical, mixtures [2,3]. Biological monitoring uses instead chemical, and/or biological variables, designed to answer selected biological responses (e.g., morphological altera- questions about environmental change” [1]. Chemical tions, cellular biomarkers, behavioral changes, etc.) deriving from environmental exposure to complex mix- * Correspondence: [email protected] tures of chemicals for evaluating exposure and health 2Banat's University of Agricultural Sciences and Veterinary Medicine from risk compared to an appropriate reference [4]. These Timisoara, Faculty of Food Processing Technology, Calea Aradului 119, RO two complementary approaches have been successfully 300645, Timisoara, Romania Full list of author information is available at the end of the article integrated in most environmental monitoring programs © 2012 Nica et al.; licensee Chemistry Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Nica et al. Chemistry Central Journal 2012, 6:55 Page 2 of 15 http://journal.chemistrycentral.com/content/6/1/55 to provide information feedback on the actual impact of included these HMs among the most dangerous sub- human-induced pollution on the environment, and to stances discharged into the natural environment. reflect the efficiency of prescribed mitigation measures The Banat region is a highly industrialized area in to protect the environment [5]. western Romania, which includes the studied areas. Besides the persistent organic pollutants, heavy metal The diverse mineral resources of this region have (HM) accumulation in air, soil, water, and biota is in- facilitated the extensive development of mining, mi- creasingly becoming a global problem with the develop- neral, and metalurgical industry, particularly in the ment of industry, mining activity, application of sewage county of Caras-Severin. Most of these industrial facil- sludge, and irrigation of waste water [2]. HM pollution ities were established under Habsburg administration of the soil is often less visible and direct than other types in the eighteenth century and continued till the end of of land pollution (e.g., garbage, refuse, littering), but its the tweentieth century (e.g., Resita, Otelu Rosu, Anina, effects on terrestrial ecosystems and humans are long- Bocsa, etc.) [17]. Long-term pollution in the county of lasting and severe [5]. HM toxicity in the environment Caras-Severin resulted in Cu, Zn, Cd, and Pb accumu- depends on several physicochemical and biological fac- lation in soil and vegetation [18]. Another major in- tors, among which HM bioavailability in soil plays a cru- dustrial area in Banat region is the town of Timisoara, cial role in their accumulation along the food chain; the largest and the most populated city from this area. therefore, this factor becomes an important issue in Recent studies occasionally revealed significant Cu, Zn, assessing the environmental quality [6]. It was also Cd, and Pb levels in air, soil, water, and vegetation in found that synergic and antagonic relationships existing Timisoara and the neighbouring areas [19]. However, between HM metal ions may increase their toxic poten- little information is available concerning the bio- tial [7,8]. Such findings are extremely important, because accumulation and the biomagnification of these HMs in the environment HMs usually co-occur in complex in terrestrial ecosystems in Romania, particularly in mixtures [9]. Banat region. Copper (Cu), zinc (Zn), cadmium (Cd), and lead Many studies [20-23] showed that land snails can con- (Pb) were chosen because they are among the most centrate high levels of Cu, Zn, Cd, and Pb in their soft common HMs which can pollute the environment, tissue without revealing any major metabolic disorders. especially in areas with high anthropogenic pressure. These HMs were found to accumulate into the snail People have been exposed to these HMs on large shell, often resulting in alterations of shell geometry or scale over the last century, and all of them are size [20,24-26]. In polluted soils Cu, Zn, Cd, and Pb are known to pose serious threats to terrestrial ecosys- taken by vegetation, and subsequently they can be trans- tems [5]. The Romanian Soil Quality regulations set fered along food chain to herbivorous organisms. In up the alert threshold level (ATV) to which these addition, Cu, Zn, Cd, and Pb accumulate in dead plant HMs accumulate in soil: Cu: 100 mg kg-1 d.w.; Zn: and animal material, and therefore, they are ingested by 300 mg kg-1 d.w.; Cd: 3 mg kg-1 d.w.; Pb: 50 mg kg-1 organisms that feed on decaying organic matter (i.e., de- d.w. – the values are expressed as miligram per kilo- tritivore organisms). Because snails act on trophic level, gram dry weight (mg kg-1 d.w.) [10]. Cu and Zn have both as herbivorous and detritivore organisms, they can essential physiological and biochemical functions in be involved in these HM biomagnification along the plants and animals [11,12], but excessive levels can food chain [22,27]. Overall, terrestrial gastropods have be damaging to environmental health [3]. For ex- the potential to be used in environmental monitoring as ample, Cu(II) ions (> 40 mg kg-1 d.w.) significanly in- model invertebrate for Cu, Zn, Cd, and Pb accumulation hibit the alfalafa (Medicago sativa L.) seed capacity in terrestrial ecosystems [28]. to germinate and grow [13] whereas exposure to high The present research investigates land snails as end- Zn levels in soil (> 500 mg kg-1 d.w.) reduce the points of Cu, Zn, Cd, and Pb transfer in a soil-plant- ability of plants to absorb iron (Fe) and manganese herbivore food chain in terrestrial ecosystems of the Banat (Mn) [14]. In contrast, Cd and Pb have no known region. It compares the accumulation of these HMs in vital or beneficial effect on organisms [15], except for eight populations of snails from habitats exposed to indus- diatoms where a Cd-based enzyme plays an essential trial pollution for more than 30 years. By recording Cu, Zn, role in regulating atmospheric carbon [16]. Pb and Cd, and Pb level in soil, plant, and snail for each popula- Cd are toxic, persistent, and non-biodegradable in tion, HM biomagnification along food chain is traced to as- the environment, and hence, they can be easy bioac- sess the potential of native gastropods to be used in cumulated and biomagnified along terrestrial food environmental monitoring studies. In addition, we have chains [5]. Because all these HMs pose a serious examined the influence of long-term of HM exposure on toxic threat to human health and ecosystem integrity, intraspecific variation in shell morphology(shell size, rela- the EU Council Directive 76/464/EEC of 4 May 1976 tive shell height, whorl number).